DbNullNode is an internal debugging aid that simply starts up a node as part
of a group. It's primarily useful for diagnosing node start up bugs, since
it enables you to start up the nodes in a group if you have the associated
log files.

If the environment does not exist, and the -createEnv is specified it will
create the environment (with the aid of helpers), using network restore to
initialize it. This behavior can be used to advantage at a Replica node if
the log files have been damaged for example and the Replica cannot proceed.
It effectively restores the environment for the Replica, which can then
proceed with the restored files using the actual application.

Similarly, if a node does not exist in the environment and -createNode is
specified, it will create a new node in either the existing environment, or
if -createEnv is specified in a new environment.

Note that the hostnames mentioned in the member database must be resolveable
before the group can start up. The hostnames can be obtained by running
DbDumpGroup. The hostnames can be "faked" on Linux, by adding appropriate
entries to /etc/hosts or cnames to the DNS.

If the hosts all use the same port, you will need to make provisions for
virtual ip addresses that are then associated with the host. On Linux this
can be done by adding an entry of the following type for each virtual ip in
/etc/network/interfaces:

Use eth0:2, eth0:3, etc for each new virtual ip that is needed. Also,
substitute the real NIC address for XX:YY:ZZ:AA:BB:CC in the iface stanza.
Be careful when modifying your machine's configuration information since it
can have unintended side-effects. So back up the above config files before
making any changes.